We do not entirely understand the various causes of autism. For some things, we have a good idea, and others, we are still learning. Some factors are environmental. Other factors are known to be genetic.
One of the newer developments is the knowledge that toxins ingested in the later part of pregnancy can increase the risk of the child developing autism. Nutrients, too, may play a role.
The Seaver Center for Autism Research and Treatment, which is part of the Icahn School of Medicine at Mount Sinai, teamed up with The Senator Frank R. Lautenberg Environmental Health Sciences Laboratory and the Karolinska Institutet in Sweden to examine the potential link between toxin and nutrient uptake during late pregnancy and early life and the risk of developing an autism spectrum disorder.
What did they use? Baby teeth.
No Tooth Fairy Here: Only Researchers
When babies are growing their teeth, even in the womb, they have a surprising similarity to trees. When baby teeth develop, they develop in layers. Similar to the rings of a tree, you can examine these layers to learn more about what the teeth were undergoing as they developed.
You can also use the rings and layers to measure time. For trees, each ring is a year. For babies, each layer of their tooth is a week.
These researchers used teeth collected as part of the RATSS study to look at the toxin and nutrient history of the children.
By examining the layers of teeth with a laser, the researchers combed through the history of the baby. The laser could “read” biomarkers left in the layers, so the researchers knew which toxins and which nutrients the baby had taken in during that week.
Sometimes with non-identical twins, and even occasionally with identical twins, one twin will develop autism and the other will not. The researchers called these discordant twins, and it is from these siblings that the researchers collected the baby teeth.
Using discordant twins and not just normal siblings, one born after the other, is important because it removes the mother's diet as a variable. For these twins, her intake was the same, and so was what her body passed along to her growing children. But still, in these cases one developed autism and the other did not.
The teeth came from twins in Sweden, which has an ongoing study called the Roots of Autism and ADHD Twin Study Sweden. Also known as RATSS, the study finds discordant twins (and non-discordant twins to use as a control group) and collects data from them for future researchers to analyze.
Exposure to lead has long been linked to psychological harm. Lead in pipes, as a sweetener in wine, and in makeup may have been a contributing factor to the decline of the Roman Empire. Lead in paint is a danger in certain old homes and buildings, and is something we have to watch out for. It is a known neurotoxin.
And lead was found in higher quantities in the teeth of children who would later develop autism.
Manganese was also examined. This element is essential for health, but some research has started to implicate it in psychological issues as well. Our bodies require manganese in trace amounts, but in large amounts it can be toxic to the central nervous system.
Either too much or too little manganese could be bad.
Zinc was the third nutrient examined. Unlike the other two, zinc is beneficial in more than just trace amounts. In fact, one of zinc's roles in the body is to aid in the elimination of heavy metals such as lead!
It is stored throughout the body and is essential for the metabolism of DNA. It helps our genes express themselves and aids our brain in learning. Too much zinc can have negative health effects, such as copper deficiency. This requires much more zinc than lead or manganese require to cause damage.
So, the researchers were looking at zinc as a positive element.
The Rings, Examined
Even in the same womb at the same time as their sibling, twins who would later develop autism showed a different spectrum of lead, manganese, and zinc than their sibling.
Most typically, the twin who would go on to develop autism showed higher levels of lead and lower levels of manganese and zinc in their teeth.
Specifically, manganese was all around lower in the twin who would develop autism both before and after birth. Zinc slowly declined in the non-affected twin, but in the affected twin dropped sharply before birth than rose after birth. Lead was all around higher for the affected twin, but was highest after birth.
Though lead, manganese, and zinc were the metals originally looked for by the researchers, they were able to measure other levels as well.
Tin was higher in the twin who would develop autism, with the levels highest before birth. Strontium was higher in the affected twin, and was highest after birth. Chromium was lower in the affected twin, and lowest before birth.
Two of the three metals the researchers were looking for remained distinctly different between the child with autism and their twin. In a seeming oversight by the researchers, exactly which two metals are not specified.
What This Means
The main benefit of this study is to open up future research. What was gained was a lot of information on the correlation between early life intake of certain metals and the development of autism. However, as is always good to remember, correlation is not causation.
Lead and other metals have long been implicated as a potential cause for autism, but recording the total exposure levels did not establish any difference between children who would develop autism and those who would not. This study, since it looked at intake levels week-by-week, was able to show a difference.
Especially helpful is that it showed that the difference was largest in the time periods which are important for neurological development of the child.
Now that it is known that lead another metal levels are different in children who will develop autism, the path has been opened for researchers to examine what genetic factors are involved and how so. While the affected children had more toxic metals in their body, why is still unknown.
The child's body may take in more of the metals, or they may take in just as much as their unaffected twin but process the metal differently. Future studies are planned.
The full title of the study is Fetal and Postnatal Metal Dysregulation in Autism, and was published in Nature Communications on June 1, 2017.
The researchers involved were Manish Arora, Abraham Reichenberg, Charlotte Willfors, Christine Austin, Chris Gennings, Steve Berggren, Paul Lichtenstein, Henrik Anckarsäter, Kristiina Tammimies, and Sven Bölte.
The study was funded by the Beatrice and Samuel A. Seaver Foundation, the National Institute of Environmental Health Sciences, the Swedish Research Council, the European Union, and several Swedish foundations.
If you are the parent of twins, the Seaver Autism Center for Research and Treatment at Mount Sinai would like to hear from you. Regardless of whether or not your children are on the autism spectrum, you can aid in future research. They are actively recruiting both identical and non-identical twins. If you would like more information about participation, please email firstname.lastname@example.org.